Interactions : אינטראקציות

4.5. Interaction with other medicinal products and other forms of interaction

Pharmacodynamic interactions
Anti-hypertensive drugs
Ritalin may decrease the effectiveness of drugs used to treat hypertension.

Use with drugs that elevate blood pressure
Ritalin should be used with caution in patients being treated with drugs that elevate blood pressure (see also paragraph on Cerebrovascular Conditions in section 4.4 Special warnings and precautions for use).
Because of possible hypertensive crisis, Ritalin is contraindicated in patients being treated (currently or within the preceding 2 weeks) with MAO-inhibitors (see section 4.3 Contraindications).

Use with alcohol
Alcohol may exacerbate the adverse CNS effects of psychoactive drugs, including Ritalin. It is therefore advisable for patients to abstain from alcohol during treatment.

Use with anaesthetics
There is a risk of sudden blood pressure and heart rate increase during surgery. If surgery is planned, Ritalin should not be taken on the day of surgery.

Use with centrally acting alpha-2 agonists (e.g. clonidine)
Serious adverse events including sudden death have been reported in concomitant use with clonidine, although no causality for the combination has been established.

Use with dopaminergic drugs
As an inhibitor of dopamine reuptake, Ritalin may be associated with pharmacodynamic interactions when co-administered with direct and indirect dopamine agonists (including 
RIT API 11APR24 V14            Page 11 of 23           reference: New Zealand Data Sheet Jan.2024 DOPA and tricyclic antidepressants) as well as dopamine antagonists (antipsychotics, e.g.
haloperidol).
Concomitant use of Ritalin with antipsychotics is not recommended due to its counteracting mechanism of action. If upon medical assessment the combination is deemed necessary, monitoring for extrapyramidal symptoms (EPS) is recommended, as the concomitant use of methylphenidate with antipsychotics may increase the risk of EPS when there is a change (increase or decrease) in dosage of either or both medications.
Use with serotonergic drugs
The concomitant use of methylphenidate and serotonergic drugs is not recommended as this may lead to the development of serotonin syndrome (see section 4.4 Special warnings and precautions for use). Methylphenidate has been shown to increase extracellular serotonin and norepinephrine and appears to have weak potency in binding serotonin transporter.

Pharmacokinetic interactions
Ritalin is not metabolized by cytochrome P450 to a clinically relevant extent. Inducers or inhibitors of cytochrome P450 are not expected to have any relevant impact on Ritalin pharmacokinetics. Conversely, the d- and l-enantiomers of methylphenidate in Ritalin did not relevantly inhibit cytochrome P450 1A2, 2C8, 2C9, 2C19, 2D6, 2E1 or 3A.
Ritalin co-administration did not increase plasma concentrations of the CYP2D6 substrate desipramine.
Case reports suggested a potential interaction of Ritalin with coumarin anticoagulants, some anticonvulsants (e.g. phenobarbital, phenytoin, primidone), phenylbutazone, and tricyclic antidepressants but pharmacokinetic interactions were not confirmed when explored at larger sample sizes. The dosage of these drugs might have to be reduced.
An interaction with the anticoagulant ethyl biscoumacetate in 4 subjects was not confirmed in a subsequent study with a larger sample size (n=12).
Other specific drug-drug interaction studies with Ritalin have not been performed in vivo.

Drug/Laboratory test
Methylphenidate may induce false positive laboratory tests for amphetamines, particularly with immunoassays screen test.